In a system for cooling the internal combustion engine provided in a vehicle, an electronically-controlled thermostat including a heater is used as a valve for switching a flow path of cooling water (see Patent Literature 1).
The thermostat is a wax thermostat which opens and closes by utilizing a volume change of wax which occurs with a temperature change. Such a thermostat opens not only when the temperature of the cooling water rises but also when the thermostat is heated by the heater.
In the technique described in Patent Literature 1, the heater is supplied with heater supply power set for each target cooling water temperature and causes the thermostat to open at the target cooling water temperature (see FIGS. 2 and 3 and others in Patent Literature 1).